Discharge apparatus for discharging materials

ABSTRACT

A discharge apparatus is disclosed for discharging materials from a container onto an open area such as a field. The apparatus includes a power discharge device which is disposed adjacent to a discharge outlet defined by the container. The arrangement is such that when the apparatus is being used to spread the materials onto the open area such as the field, the materials move from the container through the outlet towards the power discharge device for discharging the materials at a location on the field. A power source is drivingly connected to the power discharge device for rotating the power discharge device. A power sensor is provided for sensing the power supplied by the power source which is approximately the power used by the power discharge device, the power sensor generating a first signal which is correlated to the spread rate of the materials discharged.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The subject application is a continuation of co-pending patent application U.S. Ser. No. 09/394,479 filed Sep. 11, 1999 which is a continuation-in-part of U.S. Ser. No. 08/871,425 filed Jun. 9, 1997 now U.S. Pat. No. 6,024,305. All the disclosure of the aforementioned applications is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a discharge apparatus for discharging materials from a container onto an open area such as a field.

[0004] More specifically, the present invention relates to a discharge apparatus for discharging materials from a manure spreader container onto any open area such as a field.

[0005] 2. Background Information

[0006] Normally, when manure or other fertilizers are to be spread over a field to be cultivated, the manure is evenly spread over the entire surface of the field.

[0007] However, each field has inherent characteristics which make it advantageous to apply varying quantities of the fertilizer to different parts of the field.

[0008] For example, certain parts of the field such as a valley portion may have a relatively deep soil coverage whereas an elevated portion of the same field may have had much of the soil eroded therefrom thus requiring a relative increase in soil nutrient replacement.

[0009] In view of the requirements for a variable spread of manure over the area of the field, spreader programs have been developed which optimize the amount of fertilizer required for each portion of the field.

[0010] The aforementioned programs are sometimes developed by combining the results of individual soil sample analyses taken from the various portions of the field. Accordingly, a map of the field is generated together with a set spread pattern so that the amount of fertilizer is adjusted manually to correspond with the previously determined spread requirements.

[0011] Therefore, by utilizing the spreader program, a farmer is able to raise crops of uniform quality throughout the entire field under cultivation.

[0012] In recent years, satellites have enabled the accurate determination of the actual location of a spot on the surface of the earth within a few feet and to provide not only a read out of the longitude and latitude but also the elevation of such a location. Such a means for ascertaining a location is known in the art as a “global positioning system” or GPS.

[0013] The present invention combines the aforementioned GPS technology with a land survey such that the actual location of a spreader spreading material in an open area such as a field can be continuously monitored. Such a system in combination with a soil requirement survey enables the generation of a program for regulating the amount of materials spread at any location on the open area such as a field.

[0014] Accordingly, for a particular location, the soil requirement is determined from the survey “map” so that the program generates a signal which may be used to regulate the amount of materials spread to optimize crop cultivation.

[0015] More specifically, such regulation may include one or more of the following discharge regulator arrangements:

[0016] 1) Control of the power supplied from the driving motor to the discharge means.

[0017] 2) Adjusting the opening of a door between the manure container and the discharge apparatus.

[0018] 3) Regulating the land speed of the apparatus.

[0019] 4) Altering the rotational speed of a discharge auger disposed in the materials container.

[0020] Therefore, it is a primary feature of the present invention to provide a discharge apparatus that overcomes the problems associated with the prior art proposals and which makes a considerable contribution to the art of spreading materials and the like on a field.

[0021] Another feature of the present invention is the provision of a discharge apparatus that includes a variable delivery discharge controlled by a program that optimizes the materials spread pattern.

[0022] Other features and advantages of the present invention will be readily apparent to those skilled in the art by a careful consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.

SUMMARY OF THE INVENTION

[0023] The present invention relates to a discharge apparatus and method for discharging materials onto a field or open area to be cultivated.

[0024] More particularly, the present invention concerns a discharge apparatus for discharging materials from a container onto an open area such as a field. The apparatus includes a power discharge device which is disposed adjacent to a discharge outlet defined by the container. The arrangement is such that when the apparatus is being used to spread the materials onto the open area such as the field, the materials move from the container through the outlet towards the power discharge device for discharging the materials at a location on the field. A power source is drivingly connected to the power discharge device for rotating the power discharge device. A power sensor is provided for sensing the power supplied by the power source which is approximately the power used by the power discharge device, the power sensor generating a first signal which correlates to a spread rate of the materials discharged.

[0025] In another aspect of the present invention, a discharge apparatus for discharging materials from a container onto an open area such as a field, includes a power discharge means disposed adjacent to a discharge outlet defined by the container. The arrangement is such that when the apparatus is being used to spread the materials onto the open area such as the field, the materials move from the container through the outlet towards the power discharge means for discharging the materials at a location on the field.

[0026] Also, a power means is drivingly connected to the power discharge means for rotating the power discharge means.

[0027] A power sensing means senses the power supplied by the power means which is approximately the power used by the power discharge means, the power sensing means generating a first signal which is directly proportional to the spread rate of the materials discharged.

[0028] In yet another aspect of the present invention, a discharge apparatus for discharging materials from a container onto an open area such as a field includes a power discharge means disposed adjacent to a discharge outlet defined by the container. The arrangement is such that when the apparatus is being used to spread the materials onto the open area such as the field, the materials move from the container through the outlet towards the power discharge means for discharging the materials at a location on the field.

[0029] A power means is drivingly connected to the power discharge means for rotating the power discharge means.

[0030] A power sensing means senses the power supplied by the power means which is approximately the power used by the power discharge means, the power sensing means generating a first signal which is directly proportional to the spread rate of the materials discharged.

[0031] A control means is connected to the power sensing means such that the first signal is fed into the control means.

[0032] A means is connected to the control means for generating a second signal that is fed into the control means.

[0033] The control means includes a comparator circuit for comparing the first and the second signals, the comparator circuit generating a third signal based on a comparison of the first and second signals. The arrangement is such that the third signal is used for controlling the particular spread rate at which the materials are discharged so that when the container is moved across the field, the materials are discharged onto the field at an optimal spread rate.

[0034] In a further aspect of the present invention a discharge apparatus for discharging materials from a container onto an open area such as a field includes a power discharge means which is disposed adjacent to a discharge outlet defined by the container. The arrangement is such that when the apparatus is being used to spread the materials onto the open area such as the field, the materials move from the container through the outlet towards the power discharge means for discharging the materials at a location on the field.

[0035] A power means is drivingly connected to the power discharge means for rotating the power discharge means and a power sensing means senses the power supplied by the power means which is approximately the power used by the power discharge means. The power sensing means generates a first signal which is correlated to the spread rate of the materials discharged, the arrangement being such that a repeatable relationship between the power supplied and the rate of materials discharged is achieved.

[0036] Many modifications and variations of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description of a preferred embodiment of the present invention. However, such modifications and variations fall within the spirit and scope of the present invention as defined by the appended claims. Included in such modifications would be the provision of a device secured to the apparatus for continuously monitoring and analyzing the soil as the apparatus moves over the field. Such analysis could include moisture content and/or the mineral content of the soil.

[0037] Also, although the detailed description describes a load cell arrangement for sensing the tension and the amount of material discharged, those skilled in the art will appreciate that when a hydraulic motor is used for driving the power discharge means, the hydraulic power within the hydraulic motor will be directly related to the amount of materials discharged. Similarly, in the case of an electric motor drive, the electrical power supplied will be proportional to the rate of discharge of the materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a diagrammatic plan view of a survey map of a field to be cultivated;

[0039]FIG. 2 is a side elevational view partially in section of a discharge apparatus according to the present invention;

[0040]FIG. 3 is a schematic view of the discharge apparatus shown in FIG. 2;

[0041]FIG. 4 is a similar view to that shown in FIG. 2 but shows a further embodiment of the present invention;

[0042]FIG. 5 is a front end view of another embodiment of the present invention;

[0043]FIG. 6 is a similar view to that shown in FIG. 3 but shows another embodiment of the present invention;

[0044]FIG. 7 is a similar view to that shown in FIG. 3 but shows yet another embodiment of the present invention; and

[0045]FIG. 8 is a schematic representation of the discharge apparatus concept according to the present invention.

[0046] Similar reference characters refer to similar parts throughout the various embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

[0047]FIG. 1 is a diagrammatic plan view of a survey map of a field to be cultivated. The map shows a field 16 divided into portions having coordinates a-i, 1-5. The map also shows the elevation of the field. For example, coordinate e,3 is low lying and may not require as much fertilizer as portion h,2 which is at a relatively high elevation of 390 feet.

[0048]FIG. 2 is a sectional view of a discharge apparatus generally designated 10 according to the present invention.

[0049] As shown in FIG. 2, the discharge apparatus 10 is used for discharging materials 12 onto a field 16 or open area to be cultivated.

[0050] The apparatus 10 includes a power discharge means generally designated 18 which is disposed adjacent to a discharge outlet 20 defined by a container 14. The arrangement is such that when the apparatus 10 is being used to spread the materials 12 onto the open area such as the field 16, the materials 12 move from the container 14 through the outlet 20 towards the power discharge means 18 for discharge at a location such as location e,3 on the field 16 as shown in FIG. 1.

[0051] A power means generally designated 22 is drivingly connected to the power discharge means 18 for rotating the power discharge means 18 as indicated by the arrow 19.

[0052]FIG. 3 is a side elevational view partially in section of the power discharge means 18 shown in FIG. 2. As shown in FIG. 3 a power sensing means generally designated 23 is provided for sensing the power supplied by the power means 22 which is approximately the same as the power used by the power discharge means 18. The power sensing means 23 generates a first signal which is proportional to the power supplied by the power means 22 which is correlated to the amount of material discharged.

[0053] A control means generally designated 24 is connected to the power sensing means 23 such that the first signal is fed into the control means 24.

[0054] A means generally designated 28 which may be programmable is connected to the control means 24, the means 28 generating a second signal that is fed into the control means 24.

[0055] Also, the control means 24 includes a comparator circuit 25 for comparing the first and the second signals. The comparator circuit 25 generates a third signal based on a comparison of the first and second signals. The arrangement is such that the third signal is used for variably controlling the particular rate at which the materials 12 are discharged so that when the container 14 is moved across the field 16, the materials 12 are discharged.

[0056] As shown in FIGS. 2 and 3 the power discharge means 18 includes an axle 36 rotatably driven about a rotational axis 37 by the power means 22.

[0057] Also, a plurality of arms 110, 111, 112 and 113 are connected to the axle 36 as shown in FIG. 3. Each of the arms 110-113 has a first and a second end 114 and 116 respectively. Each of the first ends 114 of the arms are secured in spaced relationship along the axle 36, the arms 110-113 extending outwardly away from the axle 36 so that on rotation of the axle 36 as indicated by the arrow 19, the arms 110-113 propel the materials 12 in a direction as indicated by the arrow 38 from the container 14 and through the power discharge means 18.

[0058] As shown in FIGS. 2 and 3, the axle 36 is disposed horizontally.

[0059]FIG. 4 is a similar view to that shown in FIG. 2 but shows another embodiment of the present invention, in which the axle 36 a is disposed substantially vertically.

[0060]FIG. 5 is a front end view of yet another embodiment of the present invention. As shown in FIG. 5 a further axle 118 b is disposed parallel and spaced relative to the axle 36. Also, a further plurality of arms 110 b, 111 b, 112 b and 113 b are connected to the further axle 118 b. Each of the further arms 110 b-113 b has a first and a second end 114 b and 116 b respectively. Each of the first ends 114 b of the further arms 110 b- 113 b are secured in spaced relationship along the further axle 118 b, the further arms 110 b- 113 b extending outwardly away from the further axle 118 b so that on rotation of the further axle 118 b, the further arms 110 b-113 b cooperate with the arms 110-113 to propel the materials in a direction 38 b from the container 14 b and through the power discharge means 18 b.

[0061] As shown in FIG. 2, each of the second ends 116 of the arms 110-113 include a hammer 44.

[0062] As shown in FIG. 3, the power means 22 is a hydraulic motor.

[0063]FIG. 6 is a similar view to that shown in FIG. 3. However, FIG. 6 shows another embodiment of the present invention in which the power means 22 c is an electric motor.

[0064] Also, FIG. 7 is a similar view to that shown in FIG. 3. However, FIG. 7 shows yet another embodiment of the present invention, in which the power means 22 d is a gas engine.

[0065]FIG. 8 is a schematic representation of the power discharge apparatus concept according to the present invention.

[0066] As shown in FIG. 8, in the broadest aspect of the present invention as indicated by the dashed box 1, the power means 22 is connected to the power sensing means 23 which sends a first signal which correlates to the spread rate of the power discharge means 18.

[0067] In another aspect of the present invention, as indicated by the dashed box 2, a control means 24 is connected to the power sensing means 23 for permitting control of the spread rate.

[0068] In yet another aspect of the present invention, as indicated by the dashed box 3, a means 28 which may be programmable, is connected to the control means 24, the means 28 sending a second signal to the control means 24. A comparator circuit within the control means 24 compares the first and second signal and generates a third signal based on the comparison. The third signal is used for adjusting the spread rate of the power discharge means 18 by means of a discharge regulator apparatus 19.

[0069] As shown in FIG. 3, the apparatus 10 also includes a drive belt 118 for drivingly connecting the power means 22 to the power discharge means 18.

[0070] More specifically, the power sensing means 23 includes a driving device generally designated 120 which extends from the power means 22 to the power discharge means 18 for driving the power discharge means 18. Furthermore, a pulley 122 cooperates with the driving device 120 such that the pulley 122 bears against the driving device 120.

[0071] A load cell 124 is disposed adjacent to the pulley 122 such that as the pulley 122 bears against the driving device 120, the load cell 124 senses a change in tension of the driving device 120. The change in tension is proportional to the power supplied by the power means 22 so that the load cell 124 generates the first signal which is proportional to the power supplied by the power means 22.

[0072] As shown in FIG. 3, the driving device 120 is a belt drive 119. However, in another embodiment of the present invention as shown in FIG. 7, the driving device 120 is a chain drive 121.

[0073] In one embodiment of the present invention as shown in FIG. 3, the control means 24 is an electronic control.

[0074] However, in the embodiment as shown in FIG. 7, the control means 24 d is a hydraulic control circuit.

[0075] The means 28 in one embodiment of the invention includes a prerecorded memory which generates the second signal which is unique to a soil analysis of the location such as e,3 on the field 16 as shown in FIG. 1.

[0076] A global positioning system 126 is provided for determining when the power discharge means 18 is disposed over the location such as e,3 on the field 16, the second signal being triggered when the location such as e,3 on the field is determined by the global positioning system 126 so that the materials 12 are discharged at the particular rate at the location such as e,3 on the field.

[0077] More specifically, the prerecorded memory may be a magnetic tape 128 or other means for storing information which is compiled from data supplied from the soil analysis for a plurality of locations such as e,3 and h,2 and other locations within the field as shown in FIG. 1.

[0078] Also, the global positioning system 126 operates in conjunction with source of information 128 such that when the global positioning system 126 determines that the power discharge means 18 is disposed in a vicinity of one of the locations such as e,3 of the plurality of locations e,3, h,2, the source of information 128 is operative to supply the second signal which is unique to the one of the locations such as e,3 so that the second signal is fed to the comparator circuit 25 for assisting in varying the power discharge means 18 to correspond with the soil analysis for the one location such as e,3 such that the particular rate of discharge is achieved.

[0079] The first signal also is compared by the comparator circuit 25 so that if a consistency of the material 12 being discharged varies, the comparator circuit 25 compares the first and second signals and generates the third signal based on the comparison of the first and second signals, the third signal controlling the rate of discharge of the materials 12 so that such rate is commensurate with the consistency of the material 12 and so that such rate corresponds with the soil analysis for the one location such as e,3.

[0080] More particularly, when manure is being spread on a field, such manure may be in liquid, semi-liquid, slurry, semi-solid or solid form. Such difference in consistency of the manure is known in the art as the “material factor” or MF. When manure is being spread, rotation of the power discharge means requires a different power input from the drive means when spreading liquid manure as compared to spreading a heavier manure. In the case of a liquid manure, the tension in the drive belt could be more than when spreading a solid material, depending on the amount being spread. The tension would be related to the amount of material being discharged. Hence, the tension of the drive belt measured by the load cell is related to the discharge rate and type of the manure. Accordingly, the rate of discharge can be varied in accordance with the nutritional value of the particular consistency of manure being spread.

[0081] The programmable means 28 in a preferred embodiment of the present invention includes means for storing data corresponding to information received from a survey of the field 16. It will also be understood by those skilled in the art that manual means could be used as an alternative arrangement instead of the programmable means.

[0082] The survey includes a combined global positioning system 126 and soil analysis survey.

[0083] Such survey may include any or all of the following information: Topography, moisture, soil type, crop yield, fertility.

[0084] Also, it will be understood by those skilled in the art that a LORAN type of system or an ACCUTRAK system is included in the generic term GPS.

[0085] Also, in the present invention, the first signal from the load cell can be used to alter the door opening of the power discharge means so as to maintain a constant spread rate when the revolutions per minute of the power means remains constant.

[0086] Additionally, the apparatus according to the present invention senses what is discharged so that the first signal from the sensor can be used to monitor the spread rate.

[0087] Furthermore, control of the spread rate is based on the weight of the materials spread and in most applications, an operator will know how much material can be spread on the field in accordance with government regulations. The operator will also know the category of material being spread. Accordingly, a constant spread rate can be maintained by automatically adjusting the door opening by means of a hydraulic drive or screw jack or any other method of controlling the spread rate.

[0088] The present invention enables an operator to automatically or manually vary the amount of fertilizer spread over different parts of a field to optimize crop cultivation while minimizing cost. 

What is claimed is:
 1. In a nutrient material spreader comprising a main frame supported on ground engaging wheels, a tank mounted on said frame for receiving material to be distributed, a conveyor, a conveyor drive motor for driving the conveyor so that the conveyor conveys material received in said tank to a discharge area, an opening in said tank in the vicinity of said discharge area, and at least one slinger driven by a slinger motor and mounted outside said tank for receiving material discharged through said opening and dispersing the material on a field as the tank is transported over the field, the improvement comprising: a control system responsive to a nutrient demand signal for controlling the speed of the auger drive motor so that nutrient material is conveyed to said opening at a rate such that a desired weight of nutrient material per unit area of the field, as specified by said nutrient demand signal, is dispersed on the field; said control system having sensing means producing feedback signals and circuit means for determining, from the feedback signals and said nutrient demand signal, the difference between the desired weight and the actual weight of nutrient material per unit area being dispersed, said circuit means producing an error signal for changing the speed of the auger drive motor to reduce said difference.
 2. The improvement as claimed in claim 1 wherein said sensing means comprises first sensor means for sensing the speed of the spreader and second sensor means for sensing the weight of said tank and the material therein.
 3. The improvement as claimed in claim 1 wherein said sensing means comprises first sensor means for sensing the speed of the spreader and second sensor means for sensing the weight of nutrient material on said slinger.
 4. The improvement as claimed in claim 1 wherein said sensing means comprises first sensor means for sensing the speed of the spreader and second sensor means for sensing the drive torque of said slinger.
 5. The improvement as claimed in claim 4 wherein said second sensor means comprises a strain sensor for sensing strain in a shaft which drives said slinger.
 6. The improvement as claimed in claim 4 wherein said second sensor means comprises a pressure sensor for sensing the driving pressure of the slinger motor.
 7. In a nutrient material spreader comprising a main frame supported on ground engaging wheels, a tank mounted on said frame for receiving material to be distributed, a conveyor assembly including an auger rotatably mounted in said tank for conveying material received in said tank to a discharge area, an opening in said tank in the vicinity of said discharge area, distribution means mounted outside said tank, including means in the vicinity of said opening for receiving material discharged through said opening and distributing it as the tank is transported over a field, the improvement comprising: a system having control means for dynamically controlling the rate at which material is distributed, said control means provided with a signal based on geographical nutrient demand data enabling site-specific distribution.
 8. In a nutrient spreader having a conveyor driven by a motor for conveying nutrient material to a slinger which disperses the nutrient material onto a field, a control system for controlling dispersal of nutrient material onto the field so that an optimum amount of nutrient is spread over each cell of the field, said control system comprising: a memory for storing a table of nutrient demand data, the table holding therein a nutrient demand value Ws corresponding to each cell of the field and defining an optimum weight of nutrient material to be spread per unit area of the corresponding cell; a global position receiver mounted on the spreader for determining which cell the spreader is currently located in, said memory being responsive to said receiver for reading out the value of Ws for the cell in which the spreader is located; and, means responsive to a value Ws read from said memory for controlling the speed of said motor.
 9. A control system as claimed in claim 8 and further comprising means for modifying each value Ws read from said memory to adjust it for nutrient value before it controls the speed of said motor.
 10. A control system as claimed in claim 8 wherein said memory holds a plurality of tables, one for each type of nutrient which might be spread, and means for operator selection of one of said tables before spreading begins.
 11. In a manure spreader having a main frame supported for transport on ground engaging wheels, a tank mounted on said frame for receiving manure to be distributed, a conveyor assembly mounted in said tank and driven by a motor for conveying manure received in said tank to a discharge area, an opening in said tank in the vicinity of said discharge area, distribution means mounted outside said tank in the vicinity of said opening for receiving manure discharged through said opening and distributing it as the tank is transported over a field at variable speed, the improvement comprising: a closed loop control system for dynamically controlling to a variable set point the rate at which manure is distributed, said closed loop control system comprising means for producing a feedback signal representing the average weight of material distributed per unit of distance traveled, and a comparator for comparing said signal to said set point to produce a control signal for controlling the speed of said motor.
 12. The improvement as claimed in claim 11 wherein said distribution means comprises at least one slinger mounted for rotation about a vertical axis and driven by a variable speed motor so as to spread manure thereon over a variable width path, and means for selecting a width of said path.
 13. The improvement as claimed in claim 11 and further comprising a source of nutrient data indicating the nutrient needs of different cells of said field, and means for deriving said set point from said source of nutrient data, said closed loop control system comprising a microprocessor having means for dividing the nutrient data by a value representing said selected width of said path.
 14. The improvement as claimed in claim 13 wherein said nutrient data is stored in a memory associated wish said microprocessor.
 15. The improvement as claimed in claim 13 and further comprising a GPS receiver for determining what cell of said field the spreader is located in.
 16. The improvement as claimed in claim 15 wherein said nutrient data is stored in a memory associated with said microprocessor and addressed by the cell location determined by said GPS receiver.
 17. The improvement as claimed in claim 11 wherein said means for producing a feedback signal comprises a speed sensor for sensing the ground speed of said spreader, weight sensing means for sensing the weight of said tank and the manure therein, and a controller including means for sampling said speed sensor and said weight sensing means to produce said feedback signal.
 18. The improvement as claimed in claim 17 wherein said controller comprises a microprocessor having means for periodically sampling said weight sensing means and determining the weight of manure distributed in a time interval between periodic samplings.
 19. The improvement as claimed in claim 11 wherein said distribution means comprises at least one slinger driven by a slinger motor to rotate about a vertical axis, and wherein said means for producing a feedback signal comprises a speed sensor for sensing the ground speed of said spreader, weight sensing means for sensing the weight of manure on said at least one slinger, and a controller including means for periodically sampling said speed sensor and said weight sensing means and producing said feedback signal.
 20. The improvement as claimed in claim 11 wherein said distribution means comprises at least one slinger mounted on a vertical shaft driven by a slinger motor, and wherein said means for producing a feedback signal comprises a speed sensor for sensing the ground speed of said spreader, a torque sensor for sensing the torque required to drive said at least one slinger, and a controller including means for periodically sampling said speed sensor and said torque sensor and producing said feedback signal.
 21. The improvement as claimed in claim 20 wherein said torque sensor comprises a strain sensor for sensing strain in said shaft.
 22. The improvement as claimed in claim 20 wherein said torque sensor comprises a pressure sensor for sensing the driving pressure of said slinger motor.
 23. The improvement as claimed in claim 11 wherein said distribution means comprises at least one slinger driven by an hydraulic slinger motor to rotate about a vertical axis, and wherein said means for producing a feedback signal comprises a speed sensor for sensing the ground speed of said spreader, a pressure sensor for sensing the pressure required to drive said at least one slinger, and a controller including means for periodically sampling said speed sensor and said pressure sensor and producing said feedback signal.
 24. The improvement as claimed in claim 11 and further comprising a manually operable control for varying said set point.
 25. A discharge apparatus for discharging materials from a container onto an open area such as a field, said apparatus comprising: a power discharge means disposed adjacent to a discharge outlet defined by the container, the arrangement being such that when the apparatus is being used to spread the materials onto the open area such as the field, the materials move from the container through said outlet towards said power discharge means for discharging the materials at a location on the field; power means drivingly connected to said power discharge means for rotating said power discharge means; and power sensing means for sensing the power supplied by the power means which is approximately the power used by said power discharge means, said power sensing means generating a first signal which is correlated to a spread rate of the materials discharged. 